Since half this thread gives workarounds, and since I had the same problem, I'll share my workaround: you can tell Google that a particular contact is your wife

Since half this thread gives workarounds, and since I had the same problem, I'll share my workaround: you can tell Google that a particular contact is your wife. There's a "relationship" field in contacts. Now I can say "call my wife" and it mostly works, although saying her name is still hopeless.